The present invention relates to a switching type motor speed regulator.
A typical prior art switching type speed regulator comprises a motor speed detection circuit comprising an AC generator coupled to a motor, a wave-shaping circuit for shaping the output from the AC generator into a rectangular waveform, a trigger pulse generator for converting this rectangular waveform output into a trigger pulse, a monostable multivibrator which is triggered by the trigger pulse from the trigger pulse generator for generating an output having a predetermined time length and a frequency dependent upon the frequency of the output signal from the AC generator, that is, the rotational speed of the motor, and an integrator for converting the AC output from the monostable multivibrator into a DC voltage which varies in response to the speed of the motor; a saw-tooth wave generator; a comparator for comparing the output from the saw-tooth wave generator with the output from the integrator and a drive circuit for generating the output signal for driving the motor in response to the output from the comparator.
When the speed of the motor exceeds a predetermined speed, the output voltage from the integrator rises so that the conduction time interval of the output transistor in the comparator becomes shorter and consequently the feed time in a switching cycle becomes shorter accordingly. As a result the speed of the motor drops. On the other hand when the speed of the motor drops below a predetermined speed, the conditions are reversed so that the speed is increased.
The average power supplied to the motor is controlled by the on-off or switching of the power to be supplied to the motor so that efficiency is very high. However as compared with the conventional speed regulators it additionally includes an oscillator or a saw-tooth wave generator so that it is complex in construction.